I will not dispute that GM, along with every other multi-line franchise i.e Ford, Chrysler, Toyota, etc, utilizes platforms. They will vary the design to appeal to as many potential customers as possible to offset the incredible tooling, R&D, and marketing costs bringing a new vehicle to market entails.
Just because two or more vehicles share a powertrain option does not make them equal, it makes them better able to be serviced though in the event of a product failure. I can tell you from my own 30+ years of GM experience, that failure rates are at an all-time low per vehicle in the GM lineup and I attribute that to superior pre-release testing and lessons learned from decades past. Warranty repairs per vehicle are fewer than Toyota and Nissan, and on par with Honda. But you never hear that on the evening news, do you? The news only puts out the negative as they see it, never anything positive about the domestic manufacturers. Pisses me off.
This is not the 70's-90's. The domestic manufacturers took quite a beating doing exactly what you point out, when the vehicles were cookie-cutter. I personally don't think a
Saab parts looks anything like a G6, nor does a G6 look like a Malibu. What ticked me off was your assertion that the H2 was a modified Tahoe, which is ludicrious given the boxed frame structural design, the first time ever electric locker, 3500 front diff, etc. None of which ever saw a Tahoe, but when pointed out to you was dismissed as "how innovative". The H2 was not built to be an innovation, it was built to be a capable off-roader with luxury attributes. I think it accomplished those goals.
Now if you want innovation, the Chevy Volt, which has been given an accelerated production date of 2010, has my interest. I am on the list for the first ones in Colorado. There are also 9 other vehicles GM is releasing over the next 3-4 years on fuel cell technology, all based on a single platform. Why? Because the platform is the basis of the R&D, to make it affordable. They will get family cars, minivans, and even an El Camino like vehicle out of this particular platform.
But you will scoff, probably bring up the EV1 and "Who killed the Electric Car" or some BS about it being all the same platform, blah blah. If you have or had family members who worked for GM at the level you claim, I'm sure they would appreciate a little loyalty. Is that asking too much?